Vocal fatigue is something you’ll have to battle when you’re doing a book signing or working a convention. The voice is created by a set of muscles and it can wear out. There are a lot of things you can do to keep it in good working order, and a lot of things you can do to hurt it. Unfortunately, there’s a lot of normal behavior that’s damaging to the voice.

Caffeine
The same things that make it a diuretic will dehydrate your throat and, combined with overuse, contribute to losing your voice. (This includes tea.)
Water is your friend.

Orange juice
Citric acid drinks–like lemonade–can cause your throat to generate mucus to protect itself. This will make you sound froggy and can lead to coughing.
Pineapple juice is your friend.

If you want a vitamin C boost, go with pineapple juice. It’s not a citrus. If you are already mucusy from a cold then try hot pineapple juice to help break up the mucus and soothe your throat. (It’s good, but you’ll have to try it to believe me)

Whispering
To create a whisper, you constrict your vocal cords and force air past them. It’s sort of the vocal version of a mute on trumpet. It’s one of the most fatiguing things you can do to your voice.

Subvocalizing is your friend.

It’s really just talking very, very quietly. You move your mouth, as if you are speaking and only let a little bit of air out.

Talking
The constant stress of speaking can just wear your voice out the same way that running a marathon can exhaust your legs. Right…but what can you do?
There’s a couple of answers to this one.

Vocal rest-When you feel your voice getting tired, stop unneeded chatter. We’ll pretend you’re fabulously successful and on a multi-city book tour. Wait until after the book-signing to call home, and then keep the call short. Don’t give in to the temptation to read your story outloud five times before your big reading.

Drink plenty of water-Like an athelete, you need to keep your instrument hydrated.

Pitch control-I can do a hundred pushups if I alternate it with other activities. Moving your voice slightly, very slightly, up or down can get it out of the area that is suffering the most fatigue. (Next time you are losing your voice, hum through your range. You’ll find that certain places are fine and others seem to be non-existant.)

Well, this post is a really good help for me, thanks for that. I’m a singer, but I don’t use my voice as my capital… Ok. but that’s another story. So, now I can understand, what my voicetrainer means, when he said to me, that water is the best thing to quench thirst and keeping the voice supple. The tip with the pineapple juice is good. i will try it, when a cold strikes me…

Glad it helps. I only learned the pineapple trick in the last couple of years, and am astounded at the difference it makes. I was always going the hot water, honey and lemon juice route, and would get coughs that stuck around forever. Not anymore.

I had a question about your experience with the timing of such measures. I’ve experimented with drinking lots of water an hour or half-hour before a performance — stage, reading, or recording — but there’s a physical need that comes with it: having to empty one’s bladder! So I also try to remember to take a bathroom break at the last possible moment before showtime. The parameters are going to be different for each type of performance (e.g., you can usually take whatever drink and pee breaks you need, whenever, during a recording session; you can drink at any time throughout a reading, but need to time your bathroom break; you may be able to go to the bathroom and drink occasionally during a stage production if you get significant off-stage breaks — or neither at all!). But have you developed any sense of the optimal time to “tank up” with liquids before a performance (maybe even optimal amount, given the inevitable pressure down below)? Or do you drink lightly but steadily throughout many hours before a performance?

(By the way, I think the word you wanted was “phlegmy” or “phlegm-y”. . . .)

I’m afraid that the answer to your question is “it depends.” Usually I try to stay hydrated in general, which I guess would be your light but steady scenario. I also drink water during the performance.